1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method for polishing a substrate, such as a semiconductor wafer, and more particularly to a polishing apparatus and a polishing method for polishing a peripheral portion of a substrate using a strip-shaped polishing tool, such as a polishing tape. The present invention also relates to a pressing member for pressing the strip-shaped polishing tool against the peripheral portion of the substrate.
2. Description of the Related Art
From a viewpoint of improving yield in fabrication of semiconductor devices, management of surface conditions of a peripheral portion of a substrate has been attracting attention in recent years. In the fabrication process of the semiconductor devices, many materials are deposited on a silicon wafer to form a multilayer structure. Therefore, unwanted films and roughened surface are formed on a peripheral portion of the substrate which is not used for products. It has been a recent trend to transport the substrate by holding only its peripheral portion using arms. Under such circumstances, the unwanted films remaining on the peripheral portion would be peeled off during various processes and could adhere to devices, causing lowered yield. Thus, a polishing apparatus for polishing the peripheral portion of the substrate has been used in order to remove the unwanted films and roughened surface therefrom.
An apparatus using a polishing tape for polishing the peripheral portion of the substrate is known as such a polishing apparatus. This type of polishing apparatus polishes the peripheral portion of the substrate by bringing a polishing surface of the polishing tape in contact with the peripheral portion of the substrate. In this specification, the peripheral portion is defined as a region including a bevel portion which is the outermost portion of the substrate and a top edge portion and bottom edge portion located radially inwardly of the bevel portion.
FIG. 1A and FIG. 1B are enlarged cross-sectional views each showing a peripheral portion of a substrate. More specifically, FIG. 1A shows a cross-sectional view of a so-called straight-type substrate, and FIG. 1B shows a cross-sectional view of a so-called round-type substrate. In the substrate W shown in FIG. 1A, the bevel portion is a portion B that is constituted by an upper slope (an upper bevel portion) P, a lower slope (a lower bevel portion) Q, and a side portion (an apex) R, all of which form an outermost circumferential surface of the substrate W. In the substrate W shown in FIG. 1B, the bevel portion is a portion B having a curved cross section and forming an outermost circumferential surface of the substrate W. The top edge portion is a flat portion E1 located radially inwardly of the bevel portion B and located radially outwardly of a region D where devices are formed. The bottom edge portion is a flat portion E2 located opposite the top edge portion and located radially inwardly of the bevel portion B. These top edge portion E1 and bottom edge portion E2 may be collectively referred to as near-edge portions.
In the conventional polishing apparatus, the polishing tape is pressed by a polishing head against the peripheral portion of the substrate to thereby polish the peripheral portion (for example, see Japanese laid-open patent publication No. 2009-154285). The polishing head has a flat pressing surface, which presses the polishing tape against the peripheral portion of the substrate, while the polishing head is inclined, to thereby polish the peripheral portion. However, it is difficult to accurately polish the top edge portion and the bottom edge portion by the flat pressing surface. For example, in the substrate shown in FIG. 1A, it is difficult to polish only the top edge portion E1 accurately along a boundary between the device region D and the top edge portion E1. In particular, when the polishing head is inclined such that the polishing tape makes an acute angle with a surface of the substrate, the devices may be damaged by the polishing tape.
Japanese laid-open patent publication No. 2009-208214 discloses a polishing apparatus having linear pressing surface. In this polishing apparatus, as shown in FIG. 2A, a pressing member 100 having the linear pressing surface is moved in a radially outward direction of the substrate W at a constant speed, while pressing a polishing tape 101 against the top edge portion of the substrate W. The polishing apparatus thus structured can polish the top edge portion without damaging the device region. However, as shown in FIG. 2B, since a distance between the linearly-extending pressing surface and the outermost circumference of the substrate W is not constant, a contact time between the polishing tape and the substrate becomes shorter in an inner edge of the top edge portion than in other regions. As a result, as shown in FIG. 2C, the inner edge of the top edge portion is scraped obliquely.